The fabrication of electronic circuit devices, particularly semiconductor devices, is well suited to batch fabrication on a single substrate usually referred to as a wafer. Separating each of these completed devices, also referred to as dice or chips in the semiconductor industry, from the wafer has often resulted in damage and contamination to the circuits. As a result, methods have been developed in the past to separate the dice with the objective of minimizing this damage and contamination.
A well known method in the semiconductor art is to scribe with a diamond tip a series of lines dividing the dice and then to flex the wafer, causing the dice to break apart. While this method has been highly refined, it still produces a significant percentage of damaged dice, especially when used with relatively larger dice, for example, in the range of 200 mils (0.20 inches, 5.08 mm) on a side. As a result, such dice are usually tested twice, once prior to separation when handling in wafer form is relatively easy; and again after separation, when each individual die must be handled, to verify that previously usable devices have not been degraded by the separation process.
A relatively new technique for separating the dice on a wafer is disclosed by F. C. Gantley in U.S. Pat. No. 4,138,304, in which the wafer is mounted on a vinyl membrane and then sawed into individual dice. The saw cuts through the wafer but not completely through the membrane, thus leaving the dice in place to allow the separated dice to be tested on a conventional wafer tester, thus obviating the need for a preseparation test.
Although severing of the wafer typically has caused the greatest amount of damage and contamination to the dice during the separation process, a significant amount of damage and contamination can occur to each die during the actual removal of each die from the wafer array after the dice have been severed apart. A conventional method shown by Gantley in FIGS. 10 and 11 is to push up each die from the bottom and, using a vacuum pick-up tool, lift from the top of each die. In this manner the die can be segregated into special holders. Alternately, U.S. Pat. No. 2,970,730 to F. W. Schwarz, discloses in FIG. 6 an apparatus for stripping the dice from an adhesive membrane by scraping the dice away from the membrane and allowing the dice to fall together into a trough. Also, M. Wiesler et al., U.S. Pat. No. 3,497,948, discloses positioning the membrane across a vertical edge such that a row of dice have their centers positioned directly over the edge. This causes the wafer to spread and expose the two edges of the dice not supported by the vertical member. An electro-magnetic tweezers then closes to pick up a die by the exposed edges in a clamping action.
Unfortunately, each of these three prior methods can result in damage and/or contamination. The Gantley method places a tool directly on the top or working side of each die exposing the die to damage from any grit or other contamination between the tool and die. Also, the die can be damaged if it is pushed up in a cocked position as often occurs with larger die sizes. Thus the push-up tool must be positioned properly and the adhesive material uniform for proper die-membrane separation.
The Schwarz method of scraping the dice from the membrane stresses and sometimes damages the die by the action of the scraping tool directly on the die, and by the force of the tool pushing the die against the die directly adjacent to it on the membrane. Moreover the collection of the dice in a trough adds another possibility of damage to the dice.
The Wiesler et al. tweezers must be precisely aligned with the die to avoid hitting and damaging the die or an adjacent die. Moreover, the gripping power of the clamp must be firm enough to lift the die from the membrane without tilting and yet loose enough to prevent damage to the die. Thus, die damage can occur from improperly adjusted tweezers.
Therefore, it can be appreciated that an apparatus and method for removing dice from a severed wafer which has a very low incidence of damage or contamination is highly desirable.